Researchers studying a type of cell found in the trillions in
our brain have made an important discovery as to how it responds to
brain injury and disease such as stroke.
A University of Bristol team has identified proteins which trigger the
processes that underlie how astrocyte cells respond to neurological
trauma.

The star-shaped astrocytes, which outnumber neurons in humans, are a
type of glial cell that comprise one of two main categories of cell
found in the brain along with neurons. The cells, which have branched
extensions that reach synapses (the connections between neurons) blood
vessels, and neighbouring astrocytes, play a pivotal role in almost all
aspects of brain function by supplying physical and nutritional support
for neurons. They also contribute to the communication between neurons
and the response to injury.

However, the cells are also known to trigger both beneficial and
detrimental effects in response to neurological trauma. When the brain
is subjected to injury or disease, the cells react in a number of ways,
including a change in shape. In severe cases, the altered cells form a
scar, which is thought to have beneficial, as well as detrimental
effects by allowing prompt repair of the blood-brain barrier, and
limiting cell death, but also impairing the regeneration of nerve fibres
and the effective incorporation of neuronal grafts - where additional
neuronal cells are added to the injured site.

The cells change shape via the regulation of a structural component of
the cell called the actin cytoskeleton, which is made up of filaments
that shrink and grow to physically manoeuvre parts of the cell. In the
lab, the team cultured astrocytes in a dish and were able to make them
change shape by chemically or genetically manipulating proteins that
control actin, and also by mimicking the environment that the cells
would be exposed to during a stroke.

By doing so the team found that very dramatic changes in cell shape were
caused by controlling the actin cytoskeleton in the in vitro stroke
model. The team also identified additional protein molecules that
control this process, suggesting that a complex mechanism is involved.

Dr Jonathan Hanley from the University's School of Biochemistry said:
"Our findings are crucial to our understanding of how the brain responds
to many disorders that affect millions of people every year. Until now,
the details of the actin-based mechanisms that control astrocyte
morphology were unknown, so we anticipate that our work will lead to
future discoveries about this important process."